Wells that have been initially perforated and then the perforations fractures eventually experience a falloff in production or start to produce sand, water or other undesirable materials. In an effort to salvage additional production from such wells, past techniques have involved sealing off the perforations and perforating the borehole wall in other locations. The plugging of the existing perforations was done with chemicals that get into the perforations and solidify or harden to close them off. The problem with such systems is the uncertainty of distribution of the material which could leave some of the existing perforations open. Another way of closing the existing perforations is to have adjacent sliding sleeves that could be moved with a shifting tool to close the existing perforations. Some issues with this method are high initial cost, the cost of the trip to operate the sleeves and the uncertainty of whether the sleeves will actually shift to a closed position or get hung up on spurs or burrs caused by the original perforating. Other ideas have included sleeve placement over existing perforations but such a method has associated costs of placing the sleeves and some uncertainties that the placement location will cover the intended perforations and even if there is coverage of the intended perforations whether the cover will be effective as a seal to close off such openings.
The uncertainties of past methods are addressed by the present invention where a string of isolators straddles the existing perforations and where no openings in the mandrel between the isolators are to be found. In this manner the existing perforations are effectively isolated so that new perforations can be made by then perforating from within the mandrel and through the isolators to open new perforations that remain isolated from the existing perforations by virtue of the fact that the new perforations were started through the isolators. The bottom hole assembly can be delivered on coiled tubing or rigid pipe and can feature an anchor to prevent axial shifting due to borehole thermal effects. Such shifting could result in closing of the newly made perforations. An alternative way to address axial shifting is to provide internal spaces in each seal assembly so that even if there is axial shifting after firing there will still be enough new perforations aligned with such spaces in the barrier element so that adequate flow rates can be obtained without undue pressure drop.
Perforating through cement inflatable packers for initial well production has been discussed in Suman USRE 30711.
The above described features and others will be more readily apparent from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention can be determined from the appended claims.